Aqueous ink has been ordinarily used as ink for recording in ink-jet recording system. Aqueous ink basically comprises a coloring matter, water and an organic solvent, and it contains water as a main solvent in consideration of an odor and a safety to human bodies and surroundings.
Further, as a coloring matter, water-soluble dyes such as acid dyes, basic dyes, reactive dyes and direct dyes are generally used.
With respect to ink for ink-jet recording and a coloring matter, the following various characteristics are required.
That is:
(1) Properties of ink, such as a viscosity, a surface tension, a specific conductivity, a density and pH are appropriate.
(2) A long-term storage stability of ink is good.
(3) A dissolution stability of a dissolution component is so high that clogging of a nozzle does not occur.
(4) A quick-drying property in a recording material is good.
(5) A recorded image is vivid, and light resistance and water resistance are good.
However, a coloring matter and ink that satisfy all these characteristics have not yet been provided.
Especially, in ordinary aqueous ink, water-soluble dyes are used. Accordingly, when water is spilled on a recorded image, a dye is eluted, and a recorded image is blotted therewith or disappeared. Thus, it is much problematic in a water resistance.
At present, various studies have been made upon focussing on the improvement of the water resistance.
For example, a method in which an organic solvent or a resin is added to ink using a pigment or an oil-soluble dye as a coloring matter or aqueous ink using a water-soluble dye has been studied. However, in case of using a pigment, there were problems that a dispersion stability was bad and a storage stability was poor, inducing clogging of a nozzle. In case of using an oil-soluble dye, an organic solvent was used, posing a problem of an environmental sanitation such as an odor, and ink blotting notably occurred, decreasing qualities of an image. Moreover, even in case of using ink containing additives, there were problems that a storage stability was poor, clogging of a nozzle occurred, and ink was not jetted well because a viscosity of ink was increased.
Recently, Japanese Patent Laid-Open No. 340835/1994 describes ink using an aqueous dispersion containing a polyester resin colored with a dye or a pigment as a disperse phase. However, a pigment still suffers from these problems. Since a dye is also poor in a compatibility with a resin, it also involves such problems that a precipitate appears in ink, a storage stability is poor and clogging of a nozzle occurs.
As stated above, the characteristics of ink used in the ink-jet recording system in particular are greatly influenced by the characteristics intrinsic to the coloring matter. Thus, the discovery of a coloring matter that satisfies these conditions is quite important.
An object of the present invention is to provide a coloring matter which is excellent in solubility into an organic solvent, water resistance, light resistance and compatibility with a resin in particular.
Another object of the present invention is to provide aqueous yellow hue ink for ink-jet recording using the same, which is excellent in water resistance, light resistance and storage stability, and which is most suited for ink-jet recording system.